Vinyl chloride resins are utilized for various applications as a typical general-purpose plastic because they are excellent in transparency, fire retardancy and chemical resistance and inexpensive. Of these, polyvinyl chloride fibers are closed to natural hairs with respect to strength, ductility, and so on and therefore, are frequently used as fibers for artificial hairs for the hair. Polyvinyl chloride fibers themselves are shrunk beyond the need due to heat in secondary processing. As means for solving this, a process of producing polyvinyl chloride fibers made of a composition containing a vinyl chloride resin and a heat resistant chlorinated vinyl chloride resin is disclosed (for example, Patent Document 1).
The polyvinyl chloride fibers of this means are one in which a component of one side is dispersed as an island component in the other component within the fibers, and the fibers are crimped by heating.
However, in the polyvinyl chloride fibers of the foregoing means, if heat of 100° C. or higher is applied for the purpose of secondary processing of the fibers, the fibers are heat shrunk beyond the need so that the processing characteristics become inferior.
For the sake of adjusting the crimping properties of fibers, a method in which the blending amount of a chlorinated vinyl chloride resin in the composition is increased, thereby lowering heat shrinkage of the resin composition itself may be considered. Originally, a vinyl chloride resin and a chlorinated vinyl chloride resin are poor in compatibility. Thus, if the blending amount of the chlorinated vinyl chloride resin is merely increased, phase separation takes place in melt-spinning fibers so that the spinning performance are deteriorated, and therefore, such is not preferable.
For the purpose of enhancing the compatibility between a vinyl chloride resin and a chlorinated vinyl chloride resin, a method of adding an ethylene-vinyl acetate/vinyl chloride graft polymer resin resulting from graft polymerization of vinyl chloride on an ethylene-vinyl acetate copolymer is disclosed (for example, Patent Document 2).
However, since the heat shrinkage of the ethylene-vinyl acetate/vinyl chloride graft polymer resin itself is equivalent to that of the vinyl chloride resin, even if the compatibility between the vinyl chloride resin and the chlorinated vinyl chloride resin is enhanced, the heat shrinkage of the resin composition itself is increased, and therefore, such is not preferable. While it is required to select a resin having itself heat resistance to some extent while enhancing the compatibility between the vinyl chloride resin and the chlorinated vinyl chloride resin, it has not reached selection of a satisfactory resin yet.
[Patent Document 1]
JP-B-60-18323
[Patent Document 2]
JP-A-10-102317